Problem 49 - Chemistry in Focus

Question

The hydrochloric acid present in toilet bowl cleaners reacts with the calcium carbonate often deposited in toilet bowls to form calcium ions, carbon dioxide, water, and chlorine ions. Write a balanced chemical equation for the reaction.

Step-by-Step Solution

Answer

The balanced chemical reaction is: CaCO3(s) + 2 HCl(aq) \rightarrow Ca^{2+}(aq) + CO2(g) + H2O(l) + 2 Cl^{-}(aq).

Step 1: Write the Unbalanced Equation

Begin by writing the chemical formulas of the reactants and products. Hydrochloric acid is HCl, and calcium carbonate is CaCO3. They react to produce calcium ions (Ca^2+), carbon dioxide (CO2), water (H2O), and chloride ions (Cl^-). The unbalanced equation is CaCO3 + HCl → Ca^2+ + CO2 + H2O + Cl^-

Step 2: Count the Atoms of Each Element

Count the number of atoms for each element on both sides of the equation. On the left (Reactants), there is 1 Ca, 1 C, and 4 H and Cl atoms (since the number of HCl molecules is not yet defined). On the right (Products), there is 1 Ca, 1 C, 2 H, 2 O, and 1 Cl atom.

Step 3: Balance the Chemical Equation

Balance the equation by adjusting the coefficients. Since HCl provides both H and Cl, and you need to have 2 Cl atoms to balance the equation, you would add a coefficient of 2 in front of HCl. The balanced equation thus becomes: CaCO3 + 2 HCl → Ca^2+ + CO2 + H2O + 2 Cl^-

Step 4: Include Physical States

For clarity, include the physical states of each compound. Assuming standard conditions, the balanced equation with states is: CaCO3(s) + 2 HCl(aq) → Ca^2+(aq) + CO2(g) + H2O(l) + 2 Cl^-(aq)

Key Concepts

Chemical Reaction

A chemical reaction is a process that involves the rearrangement of the molecular or ionic structure of substances, producing new substances with different properties. In the context of balancing a chemical equation, we're essentially detailing the transformation from reactants to products.

For example, when hydrochloric acid interacts with calcium carbonate in toilet bowl cleaners, a chemical reaction occurs, resulting in the formation of calcium ions, carbon dioxide, water, and chloride ions. Through this process, the identity and properties of the initial substances change due to the breaking and forming of chemical bonds.

Stoichiometry

Stoichiometry is the section of chemistry that deals with the quantification of reactants and products in a chemical reaction. It ensures that the equations representing chemical reactions obey the Law of Conservation of Mass, meaning that atoms are neither created nor destroyed during a chemical reaction. Thus, reactants must be consumed, and products formed in such proportion to maintain a balance.

For instance, when balancing the equation for the reaction of hydrochloric acid with calcium carbonate, stoichiometry requires that the number of atoms for each element is equal on both sides of the equation. It's a mathematical method of ensuring that all atoms accounted for in the reactants are present in the products. By adjusting coefficients before each compound accordingly, like putting a '2' in front of HCl, we satisfy the stoichiometric requirement of the reaction, which directly informs us about the quantities of substances involved.

Chemical Formula

A chemical formula represents the types and number of atoms present in a molecule of a compound. It serves as a shorthand notation to express the chemical composition and provides insight into the molecule's structure.

For example, the chemical formula of hydrochloric acid is HCl, indicating that each molecule contains one hydrogen atom bonded to one chlorine atom. In the balanced chemical equation of the toilet cleaner reaction, the chemical formulas are essential in understanding the transformation of calcium carbonate (CaCO3) into calcium ions (Ca^2+), carbon dioxide (CO2), water (H2O), and chloride ions (Cl^-). Recognizing and writing the correct chemical formulas is crucial in balancing chemical equations and therefore in studying the quantitative aspects of chemical reactions through stoichiometry.